Various types of power line filters are known in the patent literature and available on the market. These filters are useful for reducing high frequency electromagnetic interference (EMI) with the operation of electrical appliances, such as communications equipment, televisions, computers and the like. These filters are provided for reduction of conducted EMI, i.e. unwanted signals carried by the electrical current. Thus, these filters provide proteciton against conducted interference but not against interference due to radiation in the vicinity of the electrical line.
It is known from German DOS No 3148351 to provide an LC filter in a power cord for a television. It is also known to combine such a filter with a shielded power cord to provide additional protection against high frequency electromagnetic interference.
The prior art power cord filter arrangements, although they provide useful filtering do not provide as complete filtering as would be desired in many applications.
SUMMARY OF THE INVENTION
The present invention seeks to provide an improved power line cord filtering assembly which significantly increases the quality of the protection against electromagnetic interference.
There is thus provided in accordance with an embodiment of the present invention, a power line cord filtering assembly for use with an electrical device and comprising a plug adapted to be connected to electrical mains, a power line cord and filter apparatus arranged in series with said plug, power line cord and electrical device, the filter comprising a resistor apparatus, a capacitor apparatus and an inductor apparatus.
Additionally in accordance with a preferred embodiment of the invention, the inductor apparatus is connected facing the mains. Where the power line comprises phase, neutral and earth leads, an inductor preferably is provided facing the mains along each of the leads. The invention is also applicable to two wire power lines, including only phase and neutral leads.
There is further provided in accordance with an embodiment of the present, invention, a power line cord filtering assembly for use with an electrical device and comprising a plug adapted to be connected to electrical mains, a power line cord and filter apparatus arranged in series with said plug, power line cord and electrical device, the filter being connected between the plug and the power line cord, the power line cord being shielded and the shield being connected to ground only at the device side of the power line cord.
There is additionally provided in accordance with an embodiment of the present invention, a power line cord filtering assembly for use with an electrical device and comprising a plug adapted to be connected to electrical mains, a power line cord and filter apparatus arranged in series with said plug, power line cord and elecrical device, the filter being connected between the plug and the power line cord, the power line cord being shielded and the shield extending to substantially cover the plug and the filter. Preferably, the shield extends continuously from the power line and over the plug and filter so as to eliminate regions through which electromagnetic radiation can penetrate.
Preferably the connection between the shield and ground should be a low impedance connection, typically in the form of a conductor of a width of a least one cm.
Additionally in accordance with a preferred embodiment of the present invention, the capacitance between the shield and the earth lead should be at least 1000 picofarads.